In recently developed mobile audio devices, acoustic coupling between speaker and microphone during mobile telephony leads to a decreasing quality of respective audio outputs. Therefore, echo canceller applications have been developed. Such echo canceller applications are usually formed as filter units and configured to avoid an acoustic output signal of the mobile audio device to be transmitted back via the microphone to an external device that is connected with the mobile audio device. Particularly important are echo cancelation applications for closed rooms, which have the tendency to support long echoes.
Document US 2013/251169 A describes an echo canceller that includes a signal-to-echo ratio calculating unit and a residual echo suppressing unit. The signal-to-echo calculating unit computes a signal-to-echo ratio SE(n) indicating a ratio of an echo component to a received signal x(n) from a first residual signal and a second residual signal. The first residual signal is obtained using a filter coefficient sequence of an update filter, which is obtained up to the previous operation. The second residual signal is obtained using an updated filter coefficient sequence that undergoes a coefficient update which is performed, using an arbitrary update step size μ(n), on the filter coefficient sequence of the update filter, which is obtained up to the previous operation. The residual echo suppressing unit suppresses the echo component contained in the microphone input signal in accordance with the signal-to-echo ratio the signal-to-echo ratio calculating unit computes.
It is the object of the present invention to provide an improved adaptive filter unit for being used as an echo canceller.